RAID


RAID (redundant array of inexpensive [or independent] disks) is a set of two or more storage devices combined together to provide fault tolerance and/or improve performance.

Not every level of RAID is fault tolerant. Striping (RAID 0) improves the speed of the disk subsystem, but because data is stored across two drives, there is no fault tolerance; if either drive fails, all data is lost. Fault-tolerant levels of RAID include RAID 1 (mirroring), RAID 5, RAID 10, and RAID 50.

For more information about RAID levels and RAID configuration, see "Introduction to RAID," p. 600.


Although RAID levels other than RAID 0 provide some level of fault tolerance in that they protect against data loss, you still experience a loss of productivity if you need to shut down the server, remove and replace the failed drive, and rebuild the array. Generally, RAID arrays that use motherboard-integrated ATA/IDE, SATA, or SCSI host adapters are more likely to require you to perform a manual array rebuild. For true fault tolerance, you should consider RAID arrays that permit automatic rebuilding.

Transparently Rebuilding Failed Drives

To permit a server to continue to operate even in the event of a drive failure in a RAID array, your RAID solution needs to incorporate the following fault-tolerant features:

  • Hot drive sparing With this feature, a drive not currently in the array is placed in standby mode, ready to take over for a failed drive.

  • Automatic array rebuilding This feature swaps the failed drive for the hot spare drive and rebuilds the array without user intervention.

  • Hot drive swapping This feature permits failed drive replacement without shutting down the system.

Host adapters that support these features are available for ATA/IDE, SATA, and SCSI hard disks from a variety of vendors, including the following:

  • Adaptec (www.adaptec.com)

  • HighPoint Technologies, Inc. (www.highpoint.com)

  • LSI Logic (www.lsilogic.com)

  • Promise Technology (www.promise.com)

For more information about RAID troubleshooting and array rebuilding, see "Managing RAID," p. 611.





Upgrading and Repairing Servers
Upgrading and Repairing Servers
ISBN: 078972815X
EAN: 2147483647
Year: 2006
Pages: 240

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